This invention was made with United States Government support under a contract with the United States Navy. The government has certain rights in this invention.
The present invention relates generally to high current electrical connectors, and more specifically to such connectors suitable for use in connecting the poles of adjacent field coils positioned on a generator or motor rotor.
Large electrical motors and generators are used in industrial plants and processes, for generation of electrical power, and also for marine or shipboard use. In marine applications they are frequently utilized in the generation of electrical power; and in ships' propulsion systems, that is, in providing the power for driving the ships' propellers. In these and other applications, such large motors and generators are frequently subjected to repeated starts and stops. Failures of such large generators or motors are considered serious matters, and reliability of operation is a prime requirement for such machines. Failures will seriously affect operations of industrial plants and power systems, and in the case of marine applications, the ability of the ship to supply necessary power and even the ability to maneuver and maintain headway. As an example of the extreme reliability required for marine applications, customer specifications may require that marine installations meet a cyclic duty requirement of well in excess of fifty thousand starts and stops. Moreover, in order to provide assurance of meeting such stringent requirements, generators and motors have to be designed for reliable start/stop cyclic duty requirements which are well in excess of the required number. These requirements are up to 10 times the design life of existing field connectors.
The problem of repeated start/stop cycling of large generators and motors having substantial size and weight results from significant inertial and thermal forces and strains on the various components of such generators and motors. Components at a distance from the axis of the generator or motor are, for example, subjected to significant centrifugal forces in which the restrained components react against the restraint with a force directed away from the center of curvature of its path. This centrifugal force is directly related to the product of the mass of the body and its centripetal acceleration. Such forces are of particular concern in large generators and motors where components are located significant distances from the axis of rotation. Such components include field coils disposed about the rotor and restrained from moving outward away from the generator or motor axis and core by restraining means such as adhesives, coil wedges, and retaining rings and other restraining mechanisms.
Electrical connectors which connect the field coils to terminals for connection, for example, to the field coil exciter are subjected to various forces, including centrifugal force and forces tending to move the field coils relative to the rotor and to each other each time the generator or motor is started or stopped. Concern has arisen that such connectors are potential weak links in such generators and motors.
One connector designed to withstand repeated start/stop cycles utilizes a leaved structure composed of many thin copper leaves joined together to provide a single piece connector. To provide for limited movement and resist repeated stresses due to the start/stop cycles, its general configuration includes a curved or a U-shaped bend. The upper jaw of such a connector is parallel to and connected to the field coil. In such arrangements, the multiple leaves and curve extend from the field coils parallel to the axis of rotation of the generator, and the thickness of the connector parallel to the axis of rotation is much greater than the width of the jaws perpendicular to the axis of rotation. With such an arrangement the deformations and principal inertial forces generated by start/stop cycles between the field coil and the terminal are applied perpendicular to the thin curved surface, or surfaces, to tend to flex or deform the curve to absorb any movement or forces. In the case of a U-shaped member, such forces tend to move the flexible jaws relative to each other in order to absorb centrifugal forces applied across the jaws.
Such arrangements have proven effective and reliable in operation for many applications and represent conventional wisdom for such connectors. However, we have concluded, among other things, that such connectors are too flexible and will not support very high numbers of start/stop cycles of loading, even though adequate flexibility is required of such connectors. The need for the increased reliability described above, and in particular the ability to withstand significantly increased cycles of start-stop operation, and the need to withstand fatigue failures over such increased cycles, has led to the need for a more reliable connector which will withstand increased start/stop cycles.